ST. LOUIS (KSDK) - They are passed by, driven over and crawled into, but what seems to draw the most attention to manholes downtown is the steam rising from them.

"Well, the steam can come out of the MSD sewers cause there's warm air and in the sewers the water is warm and it's cold outside and it condensates so you get a little of that," explains Todd Waelterman, Director of the City of St. Louis Street Department.

The biggest clouds, however, come from underground steam lines.

"It's an 80-year-old system," Waelterman points out.

Lines that start in a building on Lenore K. Sullivan.

"The city actually has its own steam system which is managed by Veolia which is a big corporation. There's about 17 miles of network and pipe that actually feed about 100 city buildings," Waelterman adds.

It's how those buildings are heated which means you tend to see more steam in the winter.

"The steam is released to control the pressure in the lines. The colder it gets the more steam they're pushing through the more regulating they're doing so you see it a whole lot more," Waelterman says.

There are also manholes leading to water lines, sewer lines and electrical lines, but more than 120 of the man holes downtown are dedicated to steam, proving you never really know what lies beneath.